1. Field of the Invention
The present invention is directed to a class of silanated metal-pillared interlayered clays. More specifically, the present invention is directed to a class of silanated metal-pillared interlayered clays characterized by decreased surface area, pore volume and cyclohexane adsorption compared to unsilanated pillared interlayered clays.
2. Background of the Prior Art
Pillared interlayered clays are formed from naturally occurring and synthetic layered smectites such as laponite, bentonite, montmorillonite and chlorite. These silicates may be visualized as "sandwiches" composed of silicate sheets containing four layers of oxygen atoms. These "sandwiches" or platelets are stacked one upon the other to yield a clay particle. Normally this arrangement yields a repeating structure every nine or so Angstroms.
A considerable amount of research has resulted in the determination that these platelets can be further separated by as much as 30 to 40 Angstroms. This further separation is effected by an interlayering procedure. The procedure involves intercalation of various polar molecules such as water, ethylene glycol and amines. Interlayered clays prepared from naturally occurring smectites however are not suitable for general adsorbent and catalytic applications because they tend to collapse when subjected to elevated temperature.
To overcome these difficencies smectites have been synthesized into pillared interlayered clays by exchanging the cation in the natural silicate with a replacement cation. This is accomplished by swelling the smectite in a suitable suspending agent, usually water, and adding the desired replacement cation to the suspension. Although aluminum cations are most commonly employed, pillared interlayered clays may be formed from other cations. Other cations which may be employed include chromium, nickel, iron, zirconium, molybdenum, niobium and silicon. It is emphasized that this group is not exhaustive and other metal cations may also be employed.
This procedure results in the formation of a metal-pillared interlayered clay where the metal is defined by the identity of the cation. This is so because the cation introduced between clay, platelets is of larger size than the cation naturally presert in the smectite. Moreover, if the cation introduced into the smectite, to form the pillared interlayered clay, is catalytically active the so-formed metal-pillared interlayered clay can be utilized as a catalyst.
Metal-pillared interlayered clays formed in accordance with the description given above are known to be useful as adsorbents, filtration media and the like. Although there are some disclosures in the prior art directed to the use of metal-pillared interlayered clays as catalysts, this utility has been sparsely developed in the literature.
One recent publication in this area is the use of pillared interlayered clays as cracking catalysts U.S. Pat. No. 4,510,257 to Lewis et al. describes the use of a pillared clay composition which acts as a catalyst in the cracking of hydrotreated light cat cracker feed and the isomerization of hexane.
Another metal-pillared interlayered clay product that has found application as a catalyst is the montmorillonite-based hydrogenation catalyst disclosed in Israeli Pat. application No. 58,565, filed Oct. 25, 1979 and published Nov. 30, 1982. That application discloses a pillared type clay having catalytic activity in hydrogenation applications wherein a montmorillonite clay is crosslinked by a hydroxymetal polymer, preferably, a hydroxynickel polymer.
The need in the art for the development of new processes to synthesize hydrocarbon streams rich in C.sub.3-C.sub.4 hydrocarbons is well established Such hydrocarbon feeds are, of course, critical in the production of polypropylene resins. In a like vein, these hydrocarbons are utilized in the polymerization of ethylene copolymers, important in the plastics and synthetic rubber industries. Both C.sub.3 and C.sub.4 hydrocarbon feed streams also find important use as starting materials in the oligomerization to higher hydrocarbons for a myriad of uses. Thus, it is not surprising that there is a continuing demand for new and better processes to form these products.
A suggested route to provide a source of hydrocarbons is the exploitation of the well known syngas process. That is, it has been proposed that intermediates formed from methanol, which, in turn, is the product of a catalytic syngas process could serve as a readily available feedstream to produce C.sub.3 -C.sub.4 hydrocarbons. Specifically, dimethyl ether is a downstream product of methanol formed in the syngas process. Thus, it has been proposed that a route to C.sub.3-C.sub.4 hydrocarbons could come from the catalytic conversion of dimethyl ether in that it is known that the dehydration of ethers and alcohols over acidic catalysts produces hydrocarbons.
Turning again to pillared clays, it has been proposed that such materials could serve as catalysts in this application. When a metal-pillared clay catalyst is utilized in this application, it is found that a hydrocarbon product stream is produced. Although this stream is rich in C.sub.2 to C.sub.4 hydrocarbons, the concentration of C.sub.2 hydrocarbons (ethane and ethylene) is significant, requiring further separation to produce the desired C.sub.3 -C.sub.4 hydrocarbon stream product.